In recent years, it has been strongly desired to (i) increase the density and capacity of the information storage capacity of an optical recording medium, such as an optical disc, in order to record large volumes of information to the optical recording medium and (ii) reduce the size and weight of an optical pickup apparatus in order to improve the mobility of the optical pickup apparatus.
To reduce the size and weight of the optical pickup apparatus, various integrated pickups have been proposed. Many of these integrated pickups use an optical integrated unit into which optical components are integrated.
Generally, the optical integrated unit includes: a semiconductor laser that is a light source; a light dividing section which divides outgoing light from the semiconductor laser and returning light from the information recording medium such as the optical disc; a light receiving element which converts the returning light into an electric signal; and a support substrate.
Japanese Unexamined Patent Publication No. 101063/2003 (Tokukai 2003-101063, published on Apr. 4, 2003) proposes an optical integrated unit including a semiconductor laser, a light dividing section, a light receiving element, a support substrate, and an intermediate member provided between the light receiving element and the support substrate.
Referring to FIGS. 12 and 13, the following will explain the principle of this optical integrated unit and the principle of an optical information reproducing apparatus using this optical integrated unit. FIG. 13 is a diagram showing the configuration of an optical integrated unit 100. The optical integrated unit 100 includes a support substrate 101, a light dividing section 102, a semiconductor laser 103, a light receiving element 104, and a relay substrate 105 provided between the light receiving element 104 and the support substrate 101.
The light dividing section 102 is attached to one surface of the support substrate 101, and includes at least one lens, prism, and diffraction element. On another surface of the support substrate 101, the semiconductor laser 103 that is a light source, the light receiving element 104 and the relay substrate 105 are provided.
The support substrate 1 has (i) a first opening 108 for allowing a light beam, emitted from the semiconductor laser 103, to travel to the light dividing section 102 and (ii) a second opening 109 for guiding the returning light, from the information recording medium such as the optical disc, to the light receiving element 104.
The relay substrate 105 has a third opening 106 for guiding the returning light, from the information recording medium such as the optical disc, to the light receiving element 104. In addition, the relay substrate 105 includes a conductive wiring 107 on its major surface.
Next, referring to FIG. 14, the following will explain a method for assembling an integrated unit 100. The light receiving element 104 is attached to the relay substrate 105 in advance. That is, electrode terminals of the light receiving element 104 are electrically and physically connected to the wirings 107 of the relay substrate 105 via wiring ball bumps 110. Further, a small amount of ultraviolet curing resin is supplied to four corners of the light receiving element 104 and four corners of the relay substrate 105, and is cured. This assures the physical adhesive strength between the light receiving element 104 and the relay substrate 105. In the following description, the light receiving element 104 and the relay substrate 105 are termed a light receiving unit 111 as an integral unit.
The semiconductor laser 103 and the light dividing section 102 are attached to the support substrate 101 by adhesion. Further, after the positioning of the light receiving unit 111, the light receiving unit 111 is adhered to the support substrate 101 to which the light dividing section 102 and the semiconductor laser 103 are attached. This positioning is carried out by using a method for (i) emitting light from the semiconductor laser 103 to the optical disc 130, (ii) receiving returning light, from the optical disc 130, by the light receiving unit 111, and (iii) adjusting the position of the light receiving unit 111 on the basis of an output signal of the light receiving unit 111. This is termed an active alignment. The following will explain the active alignment in reference to FIG. 15. The light receiving unit 111 is moved and adjusted while being in contact with the support substrate 101 by a collet 120 at all times. Since the light receiving unit 111 is in contact with the support substrate 101 at all times, the length of a light path from the optical disc 130 to the light receiving element 104 is held constant at all times.
Moreover, the collet 120 is provided with a prober 121, and the prober 121 takes the output signal from the light receiving element 104.
As shown in FIG. 16, the light receiving element 104 includes (i) light receiving portions A, B, C, and D which receive the returning light and divide it into four, (ii) light receiving portions E, I, and F which are provided on one side of the light receiving portions A, B, C, and D, receive the returning light, and divide it into three, (iii) light receiving portions G, J, and H which are provided on another side of the light receiving portions A, B, C, and D, receive the returning light, and divide it into three, and (iv) light receiving portions K and L. Here, a focus error signal is detected by Astigmatism focus error detection and by utilizing the light received by the light receiving portions A, B, C, and D, a tracking error signal is detected by Push-Pull method and by utilizing the light received by the light receiving portions E, I, F, G, J, and H, and an RF signal is detected by utilizing the light received by the light receiving portions K and L. Here, the position of the light receiving unit 111 can be adjusted by carrying out a calculation(s) using the output signals from respective light receiving portions. That is, the following formula is used regarding a track direction that is along a recording track on the optical disc.(A+D)−(B+C)In addition, one of the following two formulas is used regarding a radial direction that is perpendicular to the recording track on the optical disc.(A+B)−(C+D)(E+G)−(F+H)Moreover, the adjustment regarding misalignment in a light axis direction is carried out by causing the semiconductor laser 103 to move in the light axis direction or by placing a spacer between the light receiving unit 111 and the support substrate 101. Thus, the assembly of the optical integrated unit is completed.
Next, referring to FIG. 12, the following will explain the optical integrated unit and the optical pickup apparatus using the optical integrated unit. The light beam emitted from the semiconductor laser 103 passes through the first opening 108 of the support substrate 101, and passes through the light dividing section 102 without change. The light beam is converted into parallel light by a collimator lens 125, and then enters into an objective lens 126. The light beam focuses on the optical disc 130 by the objective lens 126, and is reflected by the optical disc 130. The reflected light passes through the objective lens 126 and the collimator lens 125, and enters into the light dividing section 102. The light beam is reflected by a first surface 122, and changes its traveling direction to an X direction. Further, part of the light beam is reflected by a second surface 123, but the rest of the light beam passes through the second surface 123 and is reflected by a third surface 124. These reflected beams pass through a lens 127 or a lens 128, and focus on the light receiving element 104.
However, in the above-described conventional example, since the light dividing section and the light receiving element are adhered to each other via the support substrate, the thickness error of the support substrate and the thickness error of the relay substrate provided between the light receiving element and the support substrate become the length error of the light path. Therefore, it is impossible to adjust the light receiving element highly accurately. Further, since the length error of the light path causes the loss of signal, it is impossible to provide a reliable optical integrated unit and an optical pickup apparatus using this optical integrated unit.
In order to eliminate the length error of the light path, used here is a method for causing the semiconductor laser to move in the light axis direction so as to cancel the thickness error in the light axis direction. However, in this method, the semiconductor laser that is already adhered needs to be detached, and be adhered again. Therefore, the number of steps increases. On this account, it is impossible to provide an inexpensive optical integrated unit and an optical pickup apparatus using this optical integrated unit.
Further, used as another method for eliminating the length error of the light path is a method for inserting the spacer between the light receiving unit and the support substrate. However, in this method, the spacer cannot be adjusted so as to have a thickness less than its minimum thickness. Therefore, it is impossible to carry out an accurate adjustment. On this account, it is impossible to provide a reliable optical integrated unit and an optical pickup apparatus using this optical integrated unit.